The invention relates generally to antennas. In particular, the invention relates to a broadband suspended plate antenna
Rapidly developing modern wireless communication systems require antennas of small size, low cost, powerful performance, and ease of manufacture and integration. Miniature or compact antennas are suited for achieving mobility of communication units and sectorization of base station antennas. Ease of manufacture and cheap materials lower the cost of antennas in industrial applications. To meet the performance standards required by modem wireless communication systems, broadening the bandwidths of antennas is becoming increasingly necessary and challenging.
Conventional planar antennas in their basic forms, such as microstrip patch antennas, planar inverted L- or F-antennas (ILAs or IFAs), and suspended plate antennas, suffer an inherently narrow impedance bandwidth, typically of only a few percent. The narrow impedance bandwidth of conventional planar antennas limits the broadband applications of conventional planar antennas.
To alleviate the problem of narrow impedance bandwidth, some techniques have been proposed for the design of broadband planar antennas.
For microstrip patch antennas, techniques such as the addition of parasitic elements, the use of electrically thick substrates, and the introduction of matching networks have been widely used. The enhanced impedance bandwidth for a single-layer single-element design is usually less than 10% for a voltage standing wave ratio (VSWR) of 2:1.
For planar ILAs or IFAs, techniques such as replacing the wire radiators of the wire ILAs or IFAs with planar radiators and/or loading material with high permittivity are usually employed. The improved impedance bandwidth is also approximately 10% for a VSWR of 2:1.
For suspended plate antennas with thick substrates of low dielectric constants, slotting or notching the plates as well as electromagnetic coupling between the plates and probes of the suspended plate antennas have been introduced to realise good matching conditions in broadband applications. Ameliorated impedance bandwidths are in the order of 10%xcx9c40% for a VSWR of 2:1.
However, each of the proposed techniques for alleviating the narrow impedance bandwidth problem has drawbacks.
For microstrip patch antennas, adding the parasitic elements vertically or laterally increases size, cost and complexity of manufacture. Using the electrically thick substrates increases cost and lowers radiation efficiency due to increased surface waves and dielectric loss. Introducing matching networks reduces radiation efficiency and complicates the design and fabrication of the antenna. For a single-layer single-element design, the achievable impedance bandwidth is limited, usually less than 10% for a VSWR of 2:1.
Planar ILAs or IFAs loaded with material of high permittivity suffer from large size and high cost. The achievable impedance bandwidth is approximately 10% for a VSWR of 2:1.
Suspended plate antennas have broadened impedance bandwidths in the order of 10% xcx9c40% for a VSWR of 2:1 after application of various impedance-matching techniques.
In U.S. Pat. No. 4,605,933, an impedance tab is introduced to increase the impedance bandwidth of a suspended microstrip antenna, in which part of the ground plane near the feed of the suspended microstrip antenna is raised and made parallel to the antenna""s radiator. The impedance bandwidth is increased to 70% for a VSWR of 2:1. However, the complexity of manufacture as well as the difficulty of array applications also increases as a result.
There is clearly a need for feeding structures for increasing the impedance bandwidth of suspended plate antenna.
Feeding structures for suspended plate antennas are disclosed hereinafter for enhancing the impedance bandwidth performance of such antennas. When applying any of these feeding structures, a multi-dimensional broadband impedance transformer is integrated with a suspended plate antenna. The impedance transformer electrically interconnects the radiating plate and feeding probe of the suspended plate antenna. As a result, the impedance bandwidth is increased. The multi-dimensional design of the impedance transformer is variable to allow the flexible design and adjustment of the feeding structure.
Through the multi-dimensional broadband impedance transformer, the radiating plate is fed at multiple points such as a line or an area. This feeding technique provides for the simultaneous excitement of the radiating plate in different positions even though the feeding probe is a conventional narrow or thin feeding probe.
The radiating plate may be any or combination of rectangular, circular, triangular, bow-tie-like, trapezoidal and the like geometric shape. The radiating plate may also include any or combination of vertical and lateral parasitic elements. The radiating plate may also be flat or uneven. The radiating plate may also be notched or slotted. The radiating plate may also be short-circuited by one or more pins or sheets to the ground plane of the suspended plate antenna.
The impedance transformer may be electrically connected to the probe or other signal feeding means for the radiating plate. The impedance transformer may also be notched or slotted. The impedance transformer may also be any or combination of one or more flat sheets, one or more cylinders or part thereof, and one or more symmetric or asymmetric bodies with contours of arbitrary shapes and profiles.
The ground plane may be any or combination of rectangular, circular, triangular, bow-tie-like, trapezoidal and the like geometric shape. The ground plane may also be flat or uneven. The ground plane may also be infinite or finite. The ground plane may also be notched or slotted.
The technique of simultaneously feeding the radiating plate at multiple points such as a line or an area at the different positions of the radiating plate may be applied to antenna arrays with two or more antenna elements. The feeding technique may also be used in linear polarization or circular polarization applications. The feeding scheme may also be used in broadband and multi-band, or multi-mode applications.
Therefore in accordance with a first aspect of the invention, there is disclosed hereinafter a broadband suspended plate antenna. Such an antenna comprises means for feeding signals to the antenna, a ground conductor, and a radiating element which is separated from the ground conductor. The antenna also comprises a feeding element which is electrically connected to the radiating element through a plurality of feed points on the radiating element, wherein the feeding element is electrically connected to the means for feeding signals and stacked with the radiating element and ground conductor.
In accordance with a second aspect of the invention, there is disclosed hereinafter a method for feeding a broadband suspended plate antenna having a radiating element and ground conductor. The method comprises the steps of feeding signals to the antenna, separating a radiating element from a ground conductor, and providing a feeding element and electrically connecting the feeding element to the radiating element through a plurality of feed points on the radiating element, wherein the feeding element is electrically connected to the means for feeding signals and stacked with the radiating element and ground conductor.